For the reference string 1, 2, 3, 4, 1, 2, 5, 1, 2, 3, 4, 5, FIFO causes 9 page faults with 3 frames but 10 with 4 frames. What is this called?
Correct answer D. Belady's anomaly
Explanation
Belady's anomaly is the surprising case where giving a process more frames increases its page-fault count, and FIFO is the classic algorithm that shows it. Stack algorithms such as LRU and OPT never suffer from it, because the pages held with n frames are always a subset of those held with n + 1 frames. Thrashing is a different problem caused by too few frames.
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